What are the types of dry eye?
Dry eye syndrome may be subdivided into 2 main types as follows:
- Aqueous tear-deficient dry eye is a disorder in which the lacrimal glands fail to produce enough of the watery component of tears to maintain a healthy eye surface.
- Evaporative dry eye may result from inflammation of the meibomian glands, also located in the eyelids. These glands make the lipid or oily part of tears that slows evaporation and keeps the tears stable.
The B.U.T. (Break Up Time)
The B.U.T. (Break Up Time) test evaluates tear quality by measuring how long it takes for dry spots to appear on the cornea after a blink. The Eye care practitioner applies fluorescein to the patient's eye and then observes the tear film after a blink while the patient tries to avoid the next blink. The practitioner counts by seconds until a dry spot appears. A break up time of more than 10 seconds is normal, from five to 10 seconds is marginal, and less than five seconds is low.
Three-layer Structure of Tears
Maintaining tear structure is important for the tears covering our eyes to function normally. Tears have three distinct layers from the outer surface: oil, water and mucus. Problems with any of these layers can cause dry eyes.
When the eye blinks, the lid pushes the tears across the eye into the drains (puncta) at the inner corner. The drains empty into channels (canaliculi) that connect the?eye?with the nose. The channels drain into a tear sac (lacrimal sac) that lies beside the nose. The sac narrows into the tear duct (lacrimal duct), which drains through the nasal bone into the nostril.